By correcting an optical proximity effect with respect to design patterns by an optical proximity effect correcting means and simulating patterns after the correction of optical proximity effect by a simulation means, transfer patterns of gate electrodes are generated and measurement portion in the transfer patterns of the gate electrodes are changed in accordance with characteristics required for a circuit. Then, in accordance with whether the point required from the circuit is a higher speed, stability, or a reduction of a leakage current, it is judged whether or not a deviation from the design value at the measurement point of the transfer pattern of the gate electrode as explained above is within an allowable range. The pattern of the measurement point is shifted when the deviation is not within the allowable range. By repeating feedback until the measurement point is within an allowable range, the optimum correction is performed in accordance with the characteristics required from the circuit within a range where it functions as a gate electrode.